Conventional articles of athletic footwear include two primary elements, an upper and a sole structure. The upper is usually formed from a plurality of elements, such as textiles, foam, and leather materials, that are stitched or adhesively bonded together to form an interior void for securely and comfortably receiving a foot. The sole structure incorporates multiple layers that are conventionally referred to as an insole, a midsole, and an outsole. The insole is a thin, compressible member located within the upper and adjacent a sole of the foot to enhance comfort. The midsole is secured to the upper and forms a middle layer of the sole structure. The outsole forms a ground-contacting element of the footwear and is usually fashioned from a durable, wear resistant material that includes texturing to improve traction.
The primary material forming a conventional midsole is a resilient, polymer foam, such as polyurethane or ethylvinylacetate, that extends throughout a length of the footwear. A polymer foam midsole may also incorporate a fluid-filled chamber, having the configuration of a bladder, to enhance ground reaction force attenuation of the sole structure. U.S. Pat. No. 4,183,156 to Rudy provides an example of a fluid-filled chamber that includes an outer enclosing member formed of an elastomeric material. The outer enclosing material defines a plurality of tubular members in fluid communication with each other.
The fluid-filled chamber described above may be manufactured by a two-film technique, wherein two separate layers of elastomeric film are formed to have the overall shape of the chamber. The layers are then bonded together along their respective peripheries to form an upper surface, a lower surface, and sidewalls of the chamber, and the layers are bonded together at predetermined interior locations to impart a desired shape to the chamber. That is, interior portions of the layers are connected to form subchambers of a predetermined shape and size at desired locations. The chamber is subsequently pressurized above ambient pressure by inserting a nozzle or needle, which is connected to a fluid pressure source, into a fill inlet formed in the chamber. After the chamber is pressurized, the nozzle is removed and the fill inlet is sealed.
Another method of manufacturing a fluid-filled chamber is through a blow-molding process, as generally disclosed in U.S. Pat. No. 5,353,459 to Potter et al., wherein a liquefied elastomeric material is placed in a mold having the desired overall shape and configuration of the bladder. The mold has an opening at one location through which pressurized air is provided. The pressurized air forces the liquefied elastomeric material against the inner surfaces of the mold and causes the material to harden in the mold, thereby forming a chamber with the desired shape and configuration. In addition, fluid-filled chambers may be manufactured through a thermoforming process, as disclosed in U.S. Pat. No. 5,976,451 to Skaja, et al., wherein a pair of sheets of flexible thermoplastic resin are placed against a pair of molds having a vacuum system for properly shaping the two sheets. The mold portions are then closed to seal the two sheets around their peripheries and form the bladder.
An article of footwear may also incorporate a fluid system that includes various components, including a pressure chamber, a pump chamber for increasing the pressure in the pressure chamber, one or more valves for regulating the direction and rate of fluid flow, and conduits that connect the various fluid system components. U.S. Pat. No. 6,457,262 to Swigart discloses a fluid system having a central chamber and two side chambers positioned adjacent central chamber. Each of the side chambers are in fluid communication with the central chamber through at least one conduit that includes a valve. Accordingly, a fluid contained by the fluid system may flow from the central chamber to side chambers, and the fluid may flow from the side chambers to the central chamber. Examples of other fluid systems that are sealed to prevent the entry or exit of ambient air are disclosed in Pat. Nos. 5,950,332 to Lain; U.S. Pat. No. 5,794,361 to Sadler; and 4,446,634 to Johnson et al., for example.
Fluid systems incorporated into an article of footwear may also utilize ambient air as the system fluid. U.S. Pat. No. 5,826,349 to Goss discloses an article of footwear having a fluid system that utilizes ambient air to ventilate an interior of an upper. The fluid system includes an intake positioned on the upper and a conduit leading from the intake to a plurality of chambers that are in fluid communication. Valves associated with the chambers prevent the air from escaping through the intake when the chambers are compressed. Rather, the air is forced out of the chambers through another conduit that leads to the interior of the upper. U.S. Pat. No. 5,937,462 to Huang disclose a fluid system that utilizes ambient air to pressurize a chamber within a sole structure of an article of footwear.